The present invention relates to a flexible media dispenser, particularly but not exclusively for dispensing cut sheets.
Cut sheet dispensers are well known in many devices such as printers, scanners, fax machines, automated teller machines and the like. Typically such dispensers establish differential friction between some actuating mechanism and the first and subsequent sheets. The sheet to be dispensed is slid across the adjacent sheets. In practice there is always a risk that two or more sheets will be accidentally dispensed. Much prior art focuses on detecting and correcting such anomalies.
On the other hand, attempts have been made to design mechanisms which reduce the likelihood of dispensing two sheets from the outset. One such type of mechanism is the xe2x80x98reverse bucklexe2x80x99 mechanism in which one end of the top sheet is initially driven towards its center so that the top sheet buckles. The buckled portion of the top sheet lifts away from the rest of the stack so as to facilitate removal of the top sheet. In some of these xe2x80x98reverse bucklexe2x80x99 mechanisms, the reverse driving causes one end of the top sheet to be lifted over a retaining member, so that the end can be engaged by a transport mechanism and the sheet can be dispensed. Examples of reverse buckle sheet feeders are given in GB 1 397 379 (Brooke), GB 1 410 799 (Xerox), U.S. Pat. No. 3,857,558 (Patel/Xerox), U.S. Pat. No. 3,893,663 (Sanchez/Xerox), U.S. Pat. No. 3,944,215 (Beck/Pitney Bowes), U.S. Pat. No. 4,189,138 (Kaneko/Xerox), U.S. Pat. No. 4,223,884 (Burnham/Kodak), U.S. Pat. No. 5,181,708 (Ruch/Compaq) and U.S. Pat. No. 5,195,735 (Sellers/Compaq).
The document GB 2 176 465 A (Alois Zettler) discloses a device for drawing off sheets from a sheet stack by frictionally engaging one end of the top sheet with a lower take-off roller and driving that end in the opposite direction to the final take-off direction. Unlike the reverse buckle mechanisms described above, the lower take-off roller continues to rotate in the same direction so that the end of the top sheet is lifted over the top of the lower take-off roller and is grasped by an upper take-off roller. However, it is necessary in this device to halt the lower take-off roller while a sheet is being dispensed by the upper take-off roller, so that only one sheet is dispensed at a time. The device achieves this with an arrangement of circumferential grooves in the upper and lower rollers, in which control dogs are located, so that the outer sheet is transported by engagement between the upper roller and the control dogs. The circumferential grooves and control dogs give the sheet a xe2x80x98serpentinexe2x80x99 or corrugated form, so that the device is limited to applications where protection of the sheet is not important, such as shredders.
According to a first aspect of the present invention, there is provided an apparatus or method for dispensing a outer sheet from a stack of sheets, in which the outer sheet is engaged by a rotatable member arranged so that the frictional force between the rotatable member and the stack varies as the rotatable member rotates, such that the rotatable member engages the outer sheet with a high frictional force so as to lift an end of the outer sheet away from the stack so that the rotatable member lies between the end of the outer sheet and the stack, while contacting the subsequent outer sheet with a low frictional force, or not contacting the subsequent outer sheet at all. An advantage of this arrangement is that lifting of the subsequent outer sheet at the same time as the current outer sheet is avoided.
According to a second aspect of the present invention, there is provided an apparatus or method for dispensing a outer sheet from a stack of sheets, in which one end of the outer sheet is buckled away from the stack by a rotating member until the rotating member lies between the outer sheet and the stack, and the outer sheet is then gripped between a pair of rollers, one of which may be part of the rotating member or substantially coaxial with the rotating member, while being removed from the stack. This arrangement contrasts with that of GB 2 176 465 (Alois Zettler), in which the outer sheet is grasped between an upper take-off roller and a counter-pressure device, but cannot be driven between the upper and lower take-off rollers because the lower take-off roller must be kept stationary to avoid separating another sheet from the stack while the outer sheet is still being removed. Thus, the xe2x80x98serpentinexe2x80x99 creasing of the sheets can be avoided by this aspect of the present invention.
According to a third aspect of the present invention, there is provided an apparatus or method for dispensing a outer sheet from a stack of sheets, in which the outer sheet is held at a first point against the stack with a variable frictional force and an end of the outer sheet is driven, at a second point, towards the first point so as to cause the outer sheet to buckle away from the stack, before being removed from the stack.
The variable frictional force is varied so that, during the buckling step, the frictional force is high so as to hold the outer sheet securely while it is buckled, while during the removing step, the frictional force is low so as to facilitate removal of the sheet.
According to a fourth aspect of the present invention, there is provided an apparatus and method for dispensing an outer sheet from a stack of sheets, in which an end of the outer sheet is engaged by at least part of a roller located adjacent the stack in a first position of the roller, so as to separate the end from the stack and locate the end in a space between the roller and a surface, and in a second position of the roller, the end is gripped between the roller and the surface so that the outer sheet may be removed from the stack. In its first position, the roller may be driven so as successively to separate a plurality of sheets from the stack and locate each of their ends together between the roller and the surface, before removing the plurality of sheets from the stack in the second position of the roller.
According to a fifth aspect of the present invention, there is provided an apparatus and method for dispensing a outer sheet from a stack of sheets, in which a separating member separates one end of the outer sheet from the stack, so that the separating member lies between the outer sheet and the stack, and subsequently moves towards the opposite end of the outer sheet so as to separate an intermediate portion of the outer sheet from the stack. Advantageously, this reduces the contact area between the outer sheet and the rest of the stack when the outer sheet is subsequently removed from the stack.
According to a sixth aspect of the present invention, there is provided an apparatus or method for dispensing a outer sheet from a stack of sheets, in which the outer sheet is held at an intermediate point against the stack while one end of the outer sheet is buckled away from the stack by a rotating member until the rotating member lies between the outer sheet and the rest of the stack, and the outer sheet is then removed from the stack. An advantage of holding the middle of the outer sheet against the stack during the buckling operation is that the extent of buckling of the outer sheet can be controlled so as reliably to achieve the movement of the end of the outer sheet over the rotating member.